It has now been established that when foreign compounds that undergo biotransforamtion to ester sulfates are fed to pregnant rats, fetal uptake of S-35 sulfate from the dams in impaired. Fetal retention of labelled sulfate varies with the material diet, the duration of pregnancy and the magnitude of ester sulfate excretion by the dams. It has been postulated that in late intrauterine life, sulfoconjugation of such foreign compounds by the pregnant animal occurs at the expense of the fetus. Two compounds have been fed to pregnant rats, indole and salicylamide, and these vary in their effects on fetal retention of labelled sulfate. Indole decreases the sulfate retention only in those fetuses from dams that have been maintained on low protein diets whereas the salicylamide effect is independent of diet. Projected investigations include an assessment of whether indole and salicylamide induced impairment of fetal sulfate retention is dose dependent. The causative factors which act alone or interact to decrease fetal sulfate uptake in dams that have received these foreign compounds will be studied. The site and magnitude of sulfur depletion induced in fetal rats by low protein diets with or without the addition of indole or salicylamide will be determined with particular reference to sulfated mucopolysaccharides in the skeletal tissues and skin. Risks of administering drugs which undergo sulfoconjugation in pregnancy will be evaluated.